Bootstrapping Switch Gate Protection for High-Voltage Sampling
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Solution Overview
Problem
Conventional bootstrapping switches in communication devices, such as analog-to-digital converters, suffer from premature device aging and failure due to voltage overstress, leading to issues like hot carrier injection and dielectric breakdown, especially when handling high input voltages.
Innovation Solution
The implementation of a bootstrapping switch with a diode-connected MOS transistor in the pull-down path, coupled with additional protection transistors, ensures that the gate terminal is protected from excessive voltages, allowing for quick switching between ON and OFF states without performance degradation, using a combination of series and parallel configurations to manage voltage stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional bootstrapping switches are used to sample high input voltages, then switching speed is improved, but device reliability deteriorates due to voltage overstress causing hot carrier injection and dielectric breakdown
Solution Approach 1:
A diode-connected MOS transistor is introduced as an intermediary protective element in the pull-down path of the bootstrapping switch. This intermediary component limits the voltage stress on the switching transistor by clamping the gate-to-source voltage, thereby preventing hot carrier injection and dielectric breakdown while maintaining fast switching performance
Solution Approach 2:
The protective circuitry including the diode-connected transistor and additional protection transistors is configured to preemptively limit voltage overstress before it can cause damage to the switching transistor. This prior cushioning approach prevents hot carrier injection and dielectric breakdown by ensuring the gate terminal never experiences excessive voltages, even when handling high input signals
2Reliability
If protection circuits are added to prevent voltage overstress, then device reliability is improved, but circuit complexity increases
Solution Approach 1:
The protective function is merged into the existing bootstrapping switch structure by integrating the diode-connected MOS transistor directly into the pull-down path. This combining approach allows the protection mechanism to share circuit elements with the switching function, reducing overall complexity compared to adding completely separate protection circuits
Solution Approach 2:
The diode-connected MOS transistor serves multiple functions: it acts as both a protective element limiting voltage stress and as part of the pull-down network controlling the switching action. This multi-functionality reduces the need for additional dedicated protection components, thereby limiting the increase in circuit complexity
Data Source
AI summary
Methods and systems for reliable bootstrapping switches may comprise sampling a received signal with a bootstrapping switch, where the bootstrapping switch comprises a switching metal-oxide semiconductor (MOS) transistor having a pull-down path coupled to a gate terminal of the switching MOS transistor, wherein: source terminals of both a diode-connected transistor and a second MOS transistor are coupled to the gate terminal of the switching MOS transistor; drain terminals of both the diode-connected transistor and the second MOS transistor are coupled to a source terminal of a third MOS transistor, the third MOS transistor coupled in series with a fourth MOS transistor; and a drain terminal of the fourth MOS transistor is coupled to ground. The third and fourth MOS transistors may be in series with the second MOS transistor. A gate terminal of the fourth transistor may be switched from ground to a supply voltage to activate the pull-down path.